Research Of Digital Electrode Electrical Impedance Tomography Technology

Electrical impedance tomography(EIT) is a relatively new imaging modality developed in the recent 30 years, witch has the advantages of low cost, easy portability,no radiation, functional imaging and suitable for clinical monitoring applications compared with the traditional imaging techniques such as X-ray computerized tomography (CT), magnetic resonance imaging (MRI).It is one of the important research subject in modern biomedical engineering.Its basic principle is to use different tissue, organ or the same tissue and organ in the impedance characteristics of different physiological and pathological stage (resistance or conductance) by applying different, security on the surface of the driving voltage (current), measured in response to the potential information, using the image reconstruction algorithm in the internal conductivity distribution or its change.A Digital Electrode Electrical system for electrical impedance tomography (EIT) measurement controlled by an ATmegal6 microcontroller is constructed. There are eight digital electrodes using AD5933 to measure the impedance of the targets, and the data is transmitted to the computer wirelessly by nRF24L01. The system uses impedance measurement chip AD5933, witch is highly integrated with DDS, LPF, ADC, the impedance gain amplifier, DSP microprocessor unit.The AD5933 can directly output the real and imaginary information on each frequency point through the I2C interface. And the extended peripheral circuit overcomesthe influence of DC component on incentive and the measuring to the unknown impedance, when the excitation voltage is 1.98V.It also overcomes the disadvantage ofcomplicated structure because of multiple modules, low integration, poor anti-interference ability, and simplify the data acquisition system, improve the quality of imaging.The measuring precision is affected, and the transmission distance is limited because measuring system and the computer communicate by cable. In order to eliminate the adverse effects, this paper designs a digital electrode, the upcoming AD5933 integration on the electrode, shorten the transmission distance is weak AC signal, eliminate interference, to avoid the wave reflection phenomenon; digital signal output by wireless communication, transmitted to the computer, not only realize the impedance measurement of the unknown impedance but also realize image reconstruction using Gauss Newton algorithm. The system has high integration, high accuracy, low power consumption, low cost, wireless transmission, convenient carrying and, and has wide application prospect.